In situ collection of dust grains falling from Saturn’s rings into its atmosphere

A splendid mission ended in a splendid way. Before plunging into Saturn’s atmosphere on the September 15 2017, the NASA-ESA Cassini spacecraft spent its final 22 orbits traversing the gap between the cloud tops of Saturn and its rings, exploring this unknown region for the first time. The on board Cosmic Dust Analyser was tasked to sample the ring material as well as to study how the rings interact with the host planet.

The CDA data revealed a dust environment dominated by charged nanograins roughly 10s of nanometers in size. The measured flux profile suggests that they are high-speed ejecta produced by hypervelocity impacts from the rings, on their way falling into Saturn’s atmosphere. In other words, the presence of the main rings modifies the effects of the interplanetary dust particles infall to Saturn’s atmosphere. The rings do this asymmetrically, leading to the distribution of the previously inferred “ring rain” phenomenon. We also reported the first in situ compositional analysis of material from Saturn’s main rings. Based on the elemental composition information derived from the time-of-flight mass spectrometer of CDA, two grain compositional types have been identified: water ice and silicates. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings. The observed grain composition ratio is likely shaped by processes associated with ring erosion processes and ring-planet interactions.